There was a genuine reason for Ryanair to leave BHD, and quite frankly I'm surprised that FR has remained in LDY for so long. Clearly DUB is the most lucrative airport on the island, given the huge catchment area, but FR still operate 17 destinations from ORK and 15 from SNN. And even DUB has seen routes cut - even their mega hub STN has seen dozens of routes axed; that's just the way FR operate.
Only time will tell if they expand from BFS, but simple economics states that expanding services will reduce costs, and if they were to cancel all European flights from BFS, the LGW route would ultimately be cancelled as well.